Many applications are known in the art of drive couplings which utilize features of the prior art Oldham shaft coupling to connect opposed end offset parallel members or shafts for rotation at a constant relative phase angle about respective axes. A few of many examples of couplings of this type are shown in U.S. Pat. No. 1,244,533 Morse, U.S. Pat. No. 2,932,255 Neukirch, and U.S. Pat. No. 3,404,545 Walker. All these constructions involve intermediate members connected with opposed ends of members or shafts rotatable on offset parallel axes by opposed straight guide means or keys that limit lateral motion of the intermediate members with respect to their offset members to linear paths whose axial projections intersect at right angles and cause rotation of the shafts while maintaining a fixed phase angle between them.
Devices for varying the phase angles between members rotating on offset parallel axes are also known, as shown for example in U.S. Pat. No. 4,131,096 Mitchell. Still other arrangements applicable to coaxial shafts are known such as shown in U.S. Pat. No. 2,783,589 Wiley.